On 2016-10-12 15:45, Charles Mills wrote:
> @George, thanks. I'm looking at the from a software development point of
> view, not a sysprog point of view.
> So if a shop is using an ETS and does not schedule the change then the TOD
> clock will be steered into reflecting the leap seconds, right? The TOD clock
> will slow down until it falls back to the correct time, right?
(which takes about a third of a day.)  Provided that CVTLSO was initially set
to 0.  If it's set to any other value, TIME GMT will give a correct result.
but STCK will give a surprising value.

> For a "Time Control Parameter Change event" where does the leap second get
> reflected? Still in the hardware TOD clock? It effectively stops for one
> second? Or in CVTLSO?
The latter.  z/OS adds one second to CVTLSO to "make the leap second adjustment"
while it has the CPUs spinning for one second so no user process ever perceives
an anachronistic sequence of STCK values.  The TOD clock inexorably runs at
4,096,000,000 ticks per second (as best STP can steer it).

(This would appear to be a one-second timed spin loop?.)

> -----Original Message-----
> From: George Kozakos
> Sent: Wednesday, October 12, 2016 1:29 PM
> If you do schedule the leap second, then STP generates a "Time Control
> Parameter Change event" external interrupt that gets processed by z/OS to
> make the leap second adjustment. If it is a positive change, z/OS spins on
> all CPUs for the amount of the positive leap second change to ensure there
> are no duplicate UTC time stamps and updates CVTLSO. No steering is required
> as STP UTC time remained accurate with the ETS.

-- gil

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